The past two decades have seen an explosion of interest in semiconductor nanophotonics and nanoelectronics, a large fraction enabled by controlled fabrication of epitaxial semiconductor nanostructures. See S. Kako et al., Nature Mater. 5, 887 (2006); K. J. Vahala, Nature 424, 839 (2003); and C. Weisbuch and B. Vinter, Quantum semiconductor structures: Fundamentals and applications, Elsevier (1991). At the current frontier are nanostructures in the sub-10-nm size regime; however, precise control in that size regime is extremely difficult. Coincidentally, the sub-10-nm size regime is comparable to the exciton Bohr radius in most semiconductors, and thus is also the regime in which semiconductor nanostructures exhibit quantum-size effects. See L. E. Brus, J. Chem. Phys. 80, 4403 (1984). If some aspect of a nanofabrication process were sensitive to such quantum-size effects, that process might be used to control nanostructure distribution in size much more precisely than current processes can. In fact, in pioneering work in the 1990's, Yoneyama and others showed that quantum-size effects could be used to size-selectively photo-etch non-epitaxial (colloidal) quantum dots (QDs) in solution. See H. Matsumoto et al., J. Phys. Chem. 100, 13781 (1996); T. Torimoto et al., J. Phys. Chem. B 105, 6838 (2001); D. V. Talapin et al., Conference Proceedings, 14th Indium Phosphide and Related Materials Conference (Cat. No. 02CH37307) 593 (2002); and A. van Dijken et al., Chem. Mater. 10, 3513 (1998).
The wide-bandgap III-nitrides are of broad interest in electronics and optoelectronics, many of whose device functionalities would benefit enormously from nanostructures in the quantum-size regime. See S. Nakamura, Science 281, 956 (1998); J. M. Phillips et al., Laser Photonics Rev. 1, 307 (2007); Y. Taniyasu et al., Nature 441, 325 (2006); Y. Arakawa, IEEE J. Sel. Topics Quantum Electron. 8, 823 (2002); and M. Zhang et al., Appl. Phys. Lett. 98, 221104 (2011). For example, single QDs resonantly coupled to high-Q microcavities would enable high-performance single-photon sources for quantum communications, while monodisperse ensemble QD gain media would enable lower threshold and higher efficiency visible and UV lasers of interest for displays, optical storage, and ultra-efficient and smart solid-state lighting. See S. Kako et al., Nature Mater. 5, 887 (2006); and J. J. Wierer et al., Laser Photonics Rev. 7, 963 (2013).
III-nitride materials have a combination of properties unique amongst the known semiconductors. See F. A. Ponce and D. P. Bour, Nature 386(6623), 351 (1997); Y. Arakawa, IEEE Journal of Selected Topics in Quantum Electronics 8(4): p. 823 (2002); T. Saito and Y. Arakawa, Physica E-Low-Dimensional Systems & Nanostructures 15(3), 169 (2002); S. N. Mohammad et al., Proceedings of the Ieee 83(10), 1306 (1995); M. A. Khan et al., Solid-State Electronics 41(10), 1555 (1997); and S. J. Pearton and F. Ren, Advanced Materials 12(21), 1571 (2000). Benefiting from advanced epitaxial growth technologies these materials have been widely applied to high power and high speed electronics, solid state lighting, piezoelectric sensors and actuators. However, unlike silicon semiconductors, Ill-nitrides have very high resistivity against wet chemical reactions. Wet chemical etching has only been accomplished at high temperatures with low etching rate, and without selectivity between the composited layer structures. Due to this, dry reactive ion etching has been largely applied to III-nitrides instead of wet chemical etching. See D. Zhuang and J. H. Edgar, Materials Science &Engineering R-Reports 48(1), 1 (2005); Y. Jung et al., Journal of the Electrochemical Society 159(2), H117 (2012); I. Adesida et al., Internet Journal of Nitride Semiconductor Research 4 (1999); I. M. Huygens et al., Journal of the Electrochemical Society 147(5), 1797 (2000); F. Karouta et al., Electrochemical and Solid State Letters 2(5), 240 (1999); C. B. Vartuli et al., Journal of the Electrochemical Society 143(11), 3681 (1996); C. B. Vartuli et al., Journal of the Electrochemical Society 143(10), L246 (1996); and C. B. Vartuli et al., Journal of Vacuum Science & Technology a-Vacuum Surfaces and Films 14(3), 1011 (1996). Photoelectrochemical etching has recently shown promising as an alternative wet process for gallium nitrides and its alloys. See H. Bae et al., Japanese Journal of Applied Physics 52(8), (2013); Y. Gao et al., Applied Physics Letters 84(17), 3322 (2004); C. G. Youtsey et al., Journal of Electronic Materials 27(4), 282 (1998); R. Oulton, Nature nanotechnology 9(3),169 (2014); and I. M. Huygens et al., Physical Chemistry Chemical Physics 4(11), 2301 (2002).
However, a need remains for a method to use quantum-size effects to control the fabrication of semiconductor nanostructures and, in particular, the wet chemical etching of III-nitride nanostructures.